The invention relates to an electrodynamic braking device for a universal motor.
Various embodiments of electrodynamic braking devices are known.
DE 38 25 835 A1 describes an electrical braking apparatus for a series-wound motor, having a field winding and an armature and having a circuit arrangement with phase gating control, wherein, during braking operation, the field winding is fed from the power supply system and the armature is shorted.
This braking apparatus is intended for a centrifuge, with the aim of keeping the braking torque constant over the entire rotation-speed range. The braking torque is controlled by a rotation-speed-dependent control device, with a current which is inversely proportional to the rotation speed of the electric motor being produced in the field winding of the electric motor. In addition, a braking resistor is also connected in series with the armature during braking operation.
EP 0 721 694 B1 describes an electrodynamic braking device for an electric motor, in which a power control element (4), which is connected in the main circuit of the electric motor, is connected in series, having a controller (5) which is connected to an input of the power control element and controls the motor current via the same power control element during motor or braking operation, and having a first changeover switch (13) for the armature (1) of the electric motor, with a second changeover switch (14) being connected in parallel with the armature such that the circuit which is formed by a first contact (9, 10) of the second changeover switch (14) and the armature is interrupted during motor operation and is closed during braking operation, and such that the second changeover switch (14) has a further contact (9, 11) which connects the control input of the controller (5) to a power supply system terminal (P) during motor operation, and interrupts this connection during braking operation.
In this solution, the braking current is intended to be defined via a braking resistor (15), and the field current which is drawn from the power supply system is used to produce the magnetic field for creating the braking torque, and in this case the field current is intended to be a pulsating direct current during braking, by being triggered only in every second half-cycle.
It is stated that the controller (5) controls the braking current in accordance with a predetermined field current profile, and/or that the controller (5) detects the braking current and keeps it constant by adjustment of the field current.
DE 102 34 397 A1 describes a braked series-wound motor and a method for braking the series-wound motor, according to which the series-wound motor is operated as a conventional series-wound motor during motor operation, with means for switching to braking operation allowing the armature and external excitation of a field winding to be bridged by the supply voltage, as a result of which the motor is operated as an externally excited direct-current generator for braking.
DE 28 42 145 describes a circuit arrangement for electrical braking of universal motors. When motor operation is switched off, braking operation is initiated, with the field winding still being fed from the power supply system and with the armature either being shorted or having current passed through it in the opposite direction, and with the motor being disconnected from the power supply system by a delay switch when it becomes stationary.
DE 103 17 636 A1 describes a braking device for a universal motor, in which a shorting switch (30) (triac) is provided for shorting the armature winding (18) during braking operation, with the shorting switch having a control input for determining its switching state, and with the control input of the shorting switch (30) being connected to a control unit (28) in order to carry out phase gating control of the shorting switch (30) in order to avoid brush sparking, during braking operation.
The known electrodynamic braking devices are not sufficiently suitable for the intended application.